Reuse(Struct, Enum)

It provides functional macros to reuse fields from Struct and Enum definition.

[dependencies]
born = "0.0.1"

Why this library?

You can define common fields in Rust struct and enum once and reuse them to remove code duplication. Use it when you want to reuse the same fields for the structs like the example below.

use born::{
    nested_macro,
    public_struct,
};

public_struct!(
    pub struct UserBase {
        username: String,
        email: String,
        full_name: Option<String>,
    }
);

UserBase!(
    pub struct UserIn {
        pub password: String,
    }
);

// Reuse with the same fields.
UserBase!(
    pub struct UserOut
);

UserBase!(
    pub struct UserInDB {
        pub hashed_password: String,
    }
);

Compare it with Python code below from FAST API that inspired this library.

from pydantic import BaseModel, EmailStr

class UserBase(BaseModel):
    username: str
    email: EmailStr
    full_name: str = None


class UserIn(UserBase):
    password: str

# Reuse with the same fields.
class UserOut(UserBase):
    pass


class UserInDB(UserBase):
    hashed_password: str

You can see almost same thing is done here to remove code duplication in both parts.

But, different from Python, there is no inheritance of fields with macros from born. It is lazily built(born) by your first struct or enum definition.

Everything made from them are completely irrelevant to each other execpt they share the same definition. There is no memory share or something like that.

The macros from this library are lazy struct and enum builders to remove code duplication. It is possible with the power of the Rust macro.

Examples

Here, macros to build public struct and enum are used.

If you want to build private struct and enum, just use macros that start with private and shouldn't use pub inside.

Struct

Say you build a simple demo web server to send private messages.

use born::{
    nested_macro,
    public_struct,
};

public_struct!(
    // pub is required here before struct
    pub struct MessageBase {
        pub text: String
        // pub text: String // , is not required for the struct definition.
    }
);

MessageBase!(
    #[derive(Debug, Clone, PartialEq)]
    pub struct Message {
        pub read: bool,
        // read: bool, // pub is optional.
    }
);

impl Message {
    fn update_text(&mut self, new_message: String) {
        self.text = new_message
    }
    fn read(&mut self) {
        if self.read == false {
            self.read = true;
        }
    }
}

MessageBase!(
    #[derive(Debug, Clone, PartialEq)]
    pub struct MessageCreateRequest
);

MessageBase!(
    // #[derive(Debug, Clone, PartialEq)]
    pub struct MessageUpdateRequest
);

fn main() {
    let message_create_request = MessageCreateRequest {
        text: "I am Steadylearner and 'born' is the crate name.".into(),
    };

    let mut message = Message {
        text: message_create_request.text,
        read: false,
    };
    println!("{:#?}", &message);

    assert_eq!(message, message.clone());

    let message_update_request = MessageUpdateRequest {
        text: "Reuse fields with macros from 'born'.".into(),
    };

    message.update_text(message_update_request.text);
    println!("{:#?}", &message);

    message.read();
    println!("{:#?}", &message);
}

Enum

Compare it with the code example from the Rust documenation.

use born::{
    nested_macro,
    private_enum,
};

private_enum!(
    enum WebEventBase {
        PageLoad,
        PageUnload, // , here is required if you want to extend it.
    }
);

WebEventBase!(
    // #[derive(Debug, Clone, PartialEq)]
    enum WebEvent {
        KeyPress(char),
        Click { x: i64, y: i64 },
        Paste(String),
    }
);

fn inspect(event: WebEvent) {
    match event {
        WebEvent::PageLoad => println!("page loaded"),
        WebEvent::PageUnload => println!("page unloaded"),
        WebEvent::KeyPress(c) => println!("pressed '{}'.", c),
        WebEvent::Paste(s) => println!("pasted \"{}\".", s),
        WebEvent::Click { x, y } => {
            println!("clicked at x={}, y={}.", x, y);
        },
    }
}

fn main() {
    let pressed = WebEvent::KeyPress('x');
    let pasted  = WebEvent::Paste("my text".to_owned());
    let click   = WebEvent::Click { x: 20, y: 80 };
    let load    = WebEvent::PageLoad;
    let unload  = WebEvent::PageUnload;

    inspect(pressed);
    inspect(pasted);
    inspect(click);
    inspect(load);
    inspect(unload);
}

Details

• Each struct and enum created from the macros are completely unrelevant to each other except they are built(born) from the same definition.

• When you use private_struct! and private_enum!, you can't use pub keyword in it and others use them. It wouldn't be logical if a private struct or private enum can have public fields.

• nested_macro! is required to use the other macros from this crate. It is used to make a macro that creates other macros.

macro_rules! nested_macro {
    ($($body:tt)*) => {
        macro_rules! __nested_macro { $($body)+ }
        __nested_macro!($);
    }
}

Why not attribute macro?

• You can reuse the fields with attribute macro also. But, you need some dependencies.

• If you want more, please read the official documenation about procedural macros.

How to test it

$git clone git@github.com:steadylearner/born.git && cargo test pass

1. $cargo test pass to run passing tests.
2. $cargo test fail to run failing tests. You need to install trybuild first.

If you want to see how the macros from this package expand, use $cargo test macros. You need to install rustfmt and cargo-expand to use it before.

$rustup component add rustfmt && cargo install cargo-expand

macrotest is based on trybuild. They are not that compatible to test with a single command and take long time.

They make cargo to redownload the dependendencies and recompile everytime. For that reason, there are commands to test them separately.

License